Probabilistic examination of the change in eigenfrequencies of an offshore wind turbine under progressive scour incorporating soil spatial variability

Prendergast, Luke J.; Reale, Cormac; Gavin, Kenneth

doi:10.1016/j.marstruc.2017.09.009

Cited by 46 publications

(34 citation statements)

References 49 publications

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“…supported by driven open-ended steel piles, used as single, large diameter laterally loaded monopiles or 73 multiple axially loaded piles for a jacket structure. The piles resist both the topside loads and the 74 environmental wind and wave forces (Arany et al, 2017;Prendergast et al, 2018) and efficient 75 installation is critically important to minimise time delays and prevent material damage. Piles are 76 installed using large hammers, which are usually hydraulically powered to provide a controlled driving 77…”

Section: Introduction 71mentioning

confidence: 99%

Performance of CPT-based methods to assess monopile driveability in North Sea sands

et al. 2018

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53Offshore pile driving is a high-risk activity as delays can be financially punitive. Experience of pile 54 driving for offshore jacket structures where pile diameters are typically < 2m has led to the development 55 of empirical pile driveability models with proven predictive capability. The application of these 56 methods to larger diameter piles is uncertain. A major component of driveability models involves 57 estimating the static resistance to driving, SRD, a parameter analogous to pile axial capacity. Recent 58 research on axial capacity design has led to improved models that use Cone Penetration Test, CPT data 59 to estimate pile capacity and include for the effects of friction fatigue and soil plugging. The 60 applicability of these methods to estimating pile driveability for larger diameter piles is of interest. In 61 this paper, recent CPT based axial capacity approaches, modified for mobilised base resistance and 62 ageing, are applied to estimating driveability of 4.2m diameter piles. A database of pile installation 63 records from North sea installations are used to benchmark the methods. Accounting for factors such 64as pile ageing and the relatively low displacement mobilised during individual hammer blows improves 65 the quality of prediction of pile driveability for the conditions evaluated in this study. 66 67

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Section: Introduction 71mentioning

confidence: 99%

Performance of CPT-based methods to assess monopile driveability in North Sea sands

et al. 2018

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“…It is straightforward to generate a vertical sequence of correlated random soil properties from a random field with probability distribution

F_{ξ} false(ξ false)

. For each random field realization, a vector

boldU

of uncorrelated standard Gaussian distributed variables

U_{i}

where

i = 1, 2, \dots, n

is generated.…”

Section: Geotechnical Modelsmentioning

confidence: 99%

“…32,34 It is straightforward to generate a vertical sequence of correlated random soil properties from a random field with probability distribution F ( ). 10,12,36 For each random field realization, a vector U of uncorrelated standard Gaussian distributed variables U i where i = 1, 2, … , n is generated. The dimension n corresponds to the number of depth increments in the soil-structure interaction model.…”

Section: Geotechnical Uncertainties and Random Field Modelingmentioning

confidence: 99%

Post‐installation adaptation of offshore wind turbine controls

et al. 2020

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The cost of offshore wind energy can be reduced by incorporating control strategies to reduce the support structures' load effects into the structural design process. While effective in reducing the cost of support structures, load‐reducing controls produce potentially costly side effects in other wind turbine components and subsystems. This paper proposes a methodology to mitigate these side effects at the wind farm level. The interaction between the foundation and the surrounding soil is a major source of uncertainty in estimating the safety margins of support structures. The safety margins are generally closely correlated with the modal properties (natural frequencies, damping ratios). This admits the possibility of using modal identification techniques to reassess the structural safety after installing and commissioning the wind farm. Since design standards require conservative design margins, the post‐installation safety assessment is likely to reveal better than expected structural safety performance. Thus, if load‐reducing controls have been adopted in the structural design process, it is likely permissible to reduce the use of these during actual operation. Here, the probabilistic outcome of such a two‐stage controls adaptation is analyzed. The analysis considers the structural design of a 10 MW monopile offshore wind turbine under uncertainty in the site‐specific soil conditions. Two control strategies are considered in separate analyses: (a) tower feedback control to increase the support structure's fatigue life and (b) peak shaving to increase the support structure's serviceability capacity. The results show that a post‐installation adaptation can reduce the farm‐level side‐effects of load‐reducing controls by up to an order of magnitude.

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“…A comparison among cases with different soil stiffness profiles suggests that scour-induced resonance of an OWT on a monopile is most likely to occur in loose deposits. Prendergast et al [91] recently improved the numerical model to further include the effect of spatial variability in soil properties derived from measured Cone Penetration Test (CPT) data. A stochastic ground model was developed to account for the uncertainty in soil-structure interaction stiffness for a given offshore site.…”

Section: Natural Frequency and Fatigue Life (Fl)mentioning

confidence: 99%

Local Scour around a Monopile Foundation for Offshore Wind Turbines and Scour Effects on Structural Responses

Qi¹,

Gao²

2020

Geotechnical Engineering - Advances in Soil Mechanics and Foundation Engineering

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Monopile is the most commonly used foundation type for offshore wind turbines. The local scour at a monopile foundation generated by the incoming shear flow has significant influence on both quasi-static lateral responses and dynamic responses of the monopile. This chapter focuses particularly on characterizing the local scour in both spatial and temporal scales and revealing the scour mechanisms associated with the flow field around a monopile. The predicting methods for the equilibrium scour depth and the time scale of scour are detailed under various representative flow conditions in the marine environment. The scale effect while extrapolating the results of model tests to prototype conditions is highlighted. The local scour imposes significant influence not only on the deformation and stiffness of the monopile foundation, but also on the natural frequency and fatigue life of the structure system. Monopiles with diameters up to 10 m have become a feasible option as the industry is currently advancing into deeper waters. More meticulous considerations for monopile design associated with the scour depth prediction and evaluation of scour effects are still in need to efficiently minimize the cost while remaining safety simultaneously.

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Probabilistic examination of the change in eigenfrequencies of an offshore wind turbine under progressive scour incorporating soil spatial variability

Cited by 46 publications

References 49 publications

Performance of CPT-based methods to assess monopile driveability in North Sea sands

Performance of CPT-based methods to assess monopile driveability in North Sea sands

Post‐installation adaptation of offshore wind turbine controls

Local Scour around a Monopile Foundation for Offshore Wind Turbines and Scour Effects on Structural Responses

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